As in http://arstechnica.com/information-technology/2015/08/open-source-typeface-hack-brings-design-to-source-code/ – “Combine it with an HD monitor and you can comfortably work at 6 or 7px sizes.”
I’m somewhat skeptical of that for 40-year-old+ users…but still it looks like an interesting typeface. I have yet to find anything else besides this that would be equal to or better than Consolas. It may be a good option for Mac use. However, if you look at the image below, the lack of a line spacing option in Visual Studio makes it a wash. I could, in fact, use 9-pt Consolas and still find it usable, although the height savings is only a line or so in 30! Perhaps in an IDE with a line-spacing option Hack would make more sense (or someone who is inclined to futzing with typeface editors could fork the project and create a reduced-line-height version).
On my 1920×1200 monitor, reducing Hack below 8 pt (or Consolas below 9 pt) is just not comfortable. That said, it is a highly-legible and pleasing typeface. I’ll try it out in Xcode too and see if it make a difference there.